Publications
Filter Total Items: 2073
Crustal structure along the west flank of the Cascades, western Washington Crustal structure along the west flank of the Cascades, western Washington
Knowledge of the crustal structure of the Washington Cascades and adjacent Puget Lowland is important to both earthquake hazards studies and geologic studies of the evolution of this tectonically active region. We present a model for crustal velocity structure derived from analysis of seismic refraction/wide-angle reflection data collected in 1991 in western Washington. The 280-km-long...
Authors
K.C. Miller, Gordon R. Keller, J.M. Gridley, James H. Luetgert, Walter D. Mooney, H. Thybo
No: The L.A. array is not ready for prime time No: The L.A. array is not ready for prime time
Although much interest will focus upon the temporal behavior of observed deformation, the principal justification for the SCIGN array is that within a 5‐year interval it will provide an accurate and detailed determination of the velocity field in the Los Angeles basin that can be used to identify the active faults and estimate their secular slip rates. Obviously, the accuracy of the...
Authors
James C. Savage
Reflected seismic waves and their effect on strong shaking during the 1989 Loma Prieta, California, earthquake Reflected seismic waves and their effect on strong shaking during the 1989 Loma Prieta, California, earthquake
Our data indicate that critical and postcritical reflections from crustal layers and the Moho produced increased shaking at discrete distances along the San Francisco Peninsula during the 1989 Loma Prieta earthquake. These reflections may have produced an increase in amplitude that is as much as 10 times greater than that of the direct arrival. Peak amplitude-distance patterns measured...
Authors
Rufus D. Catchings, W.M. Kohler
Airborne hunt for faults in the Portland-Vancouver area Airborne hunt for faults in the Portland-Vancouver area
Geologic hazards in the Portland-Vancouver area include faults entirely hidden by river sediments, vegetation, and urban development. A recent aerial geophysical survey revealed patterns in the Earth's magnetic field that confirm the existence of a previously suspected fault running through Portland. It also indicated that this fault may pose a significant seismic threat. This discovery...
Authors
Richard J. Blakely, Ray E. Wells, Thomas S. Yelin, Peter H. Stauffer, James W. Hendley
Comparison and contrast of processes of soil formation in the San Timoteo Badlands with chronosequences in California Comparison and contrast of processes of soil formation in the San Timoteo Badlands with chronosequences in California
The degree of soil development associated with geomorphic surfaces in the San Timoteo Badlands area (STB), California allows correlation of the surfaces. Soil development indices, based on field descriptions and laboratory analysis, provide a basis for comparison of these soils to each other and to dated soil chronosequences at Cajon Pass, Merced, and Anza, California. The soils in this...
Authors
Katherine J. Kendrick, Leslie D. McFadden
Earthquake-induced burial of archaeological sites along the southern Washington coast about A.D. 1700 Earthquake-induced burial of archaeological sites along the southern Washington coast about A.D. 1700
Although inhabited by thousands of people when first reached by Europeans, the Pacific coast of southern Washington has little recognized evidence of prehistoric human occupation. This apparent contradiction may be explained partly by geologic evidence for coastal submergence during prehistoric earthquakes on the Cascadia subduction zone. Recently discovered archaeological sites, exposed...
Authors
Steve C. Cole, Brian F. Atwater, Patrick T. McCutcheon, Julie K. Stein, Eileen Hemphill-Haley
Intermediate‐depth intraslab earthquakes and arc volcanism as physical expressions of crustal and uppermost mantle metamorphism in subducting slabs Intermediate‐depth intraslab earthquakes and arc volcanism as physical expressions of crustal and uppermost mantle metamorphism in subducting slabs
We elaborate on the well-known spatial association between axc volcanoes and Wadati Benioff zones and explore in detail their genetic relationships as dual physical expressions of slab metamorphism of the oceanic crust and uppermost mantle. At hypocentral depths less than 200 km intra slab Wadati-Benioff earthquakes tend to occur near the top surfaces of slabs. Subduction of very young...
Authors
Stephen H. Kirby, E. Robert Engdahl, Roger P. Denlinger
Earthquake technology fights crime Earthquake technology fights crime
Scientists with the U.S. Geological Survey have adapted their methods for quickly finding the exact source of an earthquake to the problem of locating gunshots. On the basis of this work, a private company is now testing an automated gunshot-locating system in a San Francisco Bay area community. This system allows police to rapidly pinpoint and respond to illegal gunfire, helping to...
Authors
John C. Lahr, Peter L. Ward, Peter H. Stauffer, James W. Hendley
Site-response maps for the Los Angeles region based on earthquake ground motions Site-response maps for the Los Angeles region based on earthquake ground motions
Ground-motion records from aftershocks of the 1994 Northridge earthquake and main-shock records from the 1971 San Fernando, 1987 Whittier Narrows, 1991 Sierra Madre, and 1994 Northridge earthquakes are used to estimate site response in the urban Los Angeles, California, area. Two frequency bands are considered, 0.5-1.5 Hz and 2.0-6.0 Hz. Instrument characteristics prevented going to...
Authors
Stephen H. Hartzell, Stephen C. Harmsen, Arthur D. Frankel, David L. Carver, Edward Cranswick, Mark E. Meremonte, John A. Michael
The Loma Prieta, California, Earthquake of October 17, 1989: Main shock characteristics The Loma Prieta, California, Earthquake of October 17, 1989: Main shock characteristics
The October 17, 1989, Loma Prieta, Calif., earthquake (0004:15.2 G.m.t. October 18; lat 37.036º N., long 121.883º W.; 19-km depth) had a local magnitude (ML) of about 6.7, a surface-wave magnitude (MS) of 7.1, a seismic moment of 2.2x1019 N-m to 3.5x1019 N-m, a source duration of 6 to 15 s, and an average stress drop of at least 50 bars. Slip occurred on a dipping fault surface about 35...
Authors
Paul A. Spudich, Gregory C. Beroza, George Choy, John Boatwright, Stephen H. Hartzell, Gordon L. Stewart, Carlos Mendoza, Stephen Horton, John G. Anderson, Andres J. Mendez, Hiroo Kanamori, Kenji Satake, Michael Lisowski, Mark Hunter Murray, Jerry L. Svarc, Grant Marshall, Ross S. Stein, Karen McNally, Gerald W. Simila, Judy G. Brown, J.L. Nabelek, Ze’ev Reches, Mark D. Zoback, Jamison Steidl, Ralph J. Archuleta, Aaron A. Velasco, Thorne Lay, Jiajun Zhang, David J. Wald, Donald V. Helmberger, Thomas H. Heaton, Chesley R. Williams, Paul Segall, Francis T. Wu, Mingdong Wu, J.W. Rudnicki
Seismic anisotropy of the crystalline crust: What does it tell us? Seismic anisotropy of the crystalline crust: What does it tell us?
The study of the directional dependence of seismic velocities (seismic anisotropy) promises more refined insight into mineral composition and physical properties of the crystalline crust than conventional deep seismic refraction or reflection profiles providing average values of P-and S-wave velocities. The alignment of specific minerals by ductile rock deformation, for instance, causes...
Authors
Wolfgang Rabbel, Walter D. Mooney